This invention relates to the field of internal combustion engine instrumentation, specifically the field of engine cylinders adapted for optical instrumentation and ease of access and cleaning.
Further improvements to the performance of internal combustion engines require greater understanding of the physical processes that occur within the combustion chamber. Those physical processes are difficult to study because they are extremely complicated and highly three dimensional. Improved experimental tools can enable more complete study of the processes.
The combustion chamber precludes the use of many diagnostic tools. The conditions within the chamber are hostile to many instruments, and the presence of an instrument can disturb the process being observed. Physical access to the chamber is typically limited. Consequently, optical diagnostics are often used in place of other approaches.
Researchers have added windows to existing engines for point measurements or to introduce an external light source. Some have added flat windows to the top of the chamber. See, e.g., Witze and Dyer, "Laser Measurement Techniques Applied to Turbulent Combustion in Piston Engines," Experiments in Fluids, 4, 1986, pp. 81-92. Another used a square bore engine to maximize window space. See Namazian et al., "Schlieren Visualization of the Flow and Density Fields in the Cylinder of a Spark Ignition Engine," SAE Paper 800044, 1980. Modifying the shape of the combustion chamber to accommodate windows creates a combustion chamber with unique flow fields, useful for studying processes but not directly applicable to the study of processes in production engines.
Other researchers have used transparent cylinders to allow flow visualization. See Bates, "A Transparent Engine for Flow and Combustion Visualization Studies," SAE Paper 880520, 1988. The transparent cylinder was made of a single sapphire crystal, and was used for flow visualization.
Bowditch added a window to the top of a piston. See Bowditch, "A New Tool for Combustion Research--A Quartz Piston Engine," SAE Transactions, 69, 1961, pp. 17-23. Modifications to allow a piston-top window do not alter the chamber processes as much as modifications to the chamber's top or shape. Certain combustion processes, for example those during cold starts, result in significant soot formation. The engine must be repeatedly disassembled for cleaning the piston-top window, making Bowditch's engine cumbersome for study of such processes.
Accordingly, there remains a continuing need for a cylinder that allows optical access to an essentially unaltered combustion chamber, suitable for use with actual combustion processes, that is amenable to rapid and repeated disassembly and cleaning.